1. Field of the Invention
This invention relates to a liquid crystal display apparatus using a TFT (thin film transistor) array substrate, and more particularly, to a liquid crystal display apparatus designed, with an aim to improve the apparatus in quality by reducing short-circuit of a storage capacitance provided in a TFT array substrate.
2. Description of Related Art
In a general liquid crystal display apparatus, an image is indicated when a voltage is applied the material for display such as liquid crystal held between two confronting substrates. Pixel electrodes are arranged in matrix at least on one of the substrates of the liquid crystal display apparatus to selectively drive the pixels by respective active elements, for example, field effect transistors (FET's) having nonlinear characteristic. Moreover, a storage capacitance is provided for each pixel to improve the image quality.
FIG. 1 is a plan view showing the structure of a TFT array substrate of one pixel used in a conventional liquid crystal display apparatus disclosed, e.g., in "Proceeding of 9 the INTERNATIONAL DISPLAY RESEARCH CONFERENCE (Japan Display '89, pp. 514-517, 1989). FIG. 2 is a cross section taken along the line A--A' of FIG. 1, and FIG. 3 is a diagram of an equivalent circuit of FIG. 1.
Referring to these drawings, numeral 1 represents a source electrode line, 2 a gate electrode line, 3 a common electrode line, 4 a gate insulating film, 5 an amorphous silicon (i) layer, 7 an amorphous silicon (n.sup.+) layer, 8 a drain electrode, 9 a pixel electrode, 10 a protecting film, 14 a transparent insulating substrate, 18 a storage capacitance, 35 a liquid crystal and 38 a counter electrode, respectively.
It will be described now how to manufacture the conventional liquid crystal display apparatus having the above-mentioned structure.
The gate electrode line 2 and common electrode line 3 of MoTa are formed on the transparent insulating substrate 14. Then, each surface of the gate electrode line 2 and common electrode line 3 is subjected to anodic oxidation. The gate insulating film 4, amorphous silicon (i) layer 5 and amorphous silicon (n.sup.+) layer 7 are successively formed and patterned thereon, and the pixel electrode 9 is formed. Thereafter, the source electrode line 1 and drain electrode 8 are formed, thereby constituting a TFT. A TFT array is composed of the TFT's and pixel electrodes 9. When the common electrode 3 and pixel electrode 9 are overlapped each other across the gate insulating film 4, the storage capacitance 18 is formed. The liquid crystal 35 is held between the TFT array substrate formed in the aforementioned manner and counter electrode substrate 38 having a color filter and a transparent conductive film, whereby the liquid crystal display apparatus is manufactured.
Since the conventional liquid crystal display apparatus has the above-described structure wherein the common electrode line 3 and pixel electrode 9 are overlapped, the production yield lowers because a storage capacitor is broken to result in short-circuit of the common electrode line 3 and drain electrode 8.
FIG. 4 illustrates a plan view showing the structure of another TFT array substrate of one pixel used in a conventional liquid crystal apparatus disclosed in, for example, Japanese Patent Application Laid-Open No. 64-26822 (1989). FIG. 5 is a cross sectional view taken along the line B--B' of FIG. 4 and FIG. 6 is a diagram of an equivalent circuit of FIG. 4. In FIGS. 4 through 6, numerals 19 and 24 represent Al a gate wiring pattern by Al and a gate electrode line at the succeeding row, respectively. Numerals 1, 2, 4, 5, 7, 8, 9, 10, 14, 18, 35 and 36 represent the same elements as in FIGS. 1 through 3.
The liquid crystal display apparatus shown in FIGS. 4-6 is manufactured in the following manner.
In the first place, the gate electrode lines 2 and 24 of Cr are formed on the transparent insulating substrate 14. Further, the gate wiring pattern 19 of Al is formed on the gate electrode line 24. Then, a TFT is formed by the gate insulating film 4, semiconductor film 5, source electrode line 1 and drain electrode 8. The TFT's constitute a TFT array along with the pixel electrodes 9. Since the gate electrode line 24 at the succeeding row has a constant potential except when it is scanned, when it is overlapped with the pixel electrode 9 across the gate insulating film 4, the storage capacitance 18 is formed. The liquid crystal 35 is sandwiched between the TFT array substrate obtained as above and counter electrode 38 having a color filter and a transparent conductive film. Thus, the liquid crystal display apparatus of FIGS. 4 through 6 is obtained.
In the conventional liquid crystal display apparatus of the above-described structure, since the gate electrode line 24 at the succeeding row serves as an electrode for the storage capacitance, the storage capacitance is broken to cause short-circuit between the gate electrode line 24 and drain electrode 8, which results in lowering the production yield.